The present invention relates to a magnetic resonance imaging apparatus (also referred to as an MRI apparatus).
An example of a conventional magnetic resonance imaging apparatus is disclosed in JP-A-2002-159466. In the MRI apparatus disclosed in this official gazette, to minimize magnetic field variations caused by external vibrations, a cooling container accommodating a superconducting coil is incorporated in a pair of upper and lower vacuum vessels and supported on an inner wall of each vacuum vessel through three stays. The superconducting coils are connected together by two first connecting tubes.
In the magnetic resonance imaging apparatus described in JP-A-2002-159466, since the vacuum vessels are supported in a cantilever fashion on a floor, the upper vacuum vessel is oscillated longitudinally and laterally because mainly of a bent structure of a second connecting tube connecting the vacuum vessels. As the vacuum vessel vibrates, the cooling container accommodated in the vacuum vessel also vibrates. Because the lower cooling container is restrained from movement by the floor surface, an amplitude of oscillation of the lower cooling container is smaller than that of the upper cooling container. As a result, the superconducting coils installed in the upper and lower cooling containers are displaced relative to each other. When the upper and lower superconducting coils move relative to each other, a magnetic resonance image deteriorates. Particularly when a static magnetic field strength and an gradient magnetic field strength of an gradient magnetic field coil are increased to enhance an image quality, the oscillations of the gradient magnetic field coil used to intensify the magnetic fields significantly affect the magnetic resonance image.